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Color instability of anodized aluminum

Our company uses an aluminum part with both chem film and anodized surfaces. Upon heating, I have noticed that the black surface on some of the parts may change to purple, bronze, or gold. Does this suggest that the anodized surface is not properly sealed and is slowly leaching color from the opposite side? Or, does this mean that both coatings are really suspect?

Thank you for the help!

Rick Burkholder
infrared technologies - Dallas, Texas

Rick,

You should have mentioned what temperature you were heating these parts up to. Chromate typically breaks down around 150F, and..I believe most black dyes will start to break down around 250 F.

Marc Green
anodizer - Boise, Idaho

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